Old thread, still would like to chime in.
I'd say koto/limba top ply is not the biggest factor.
As I returning player I got some EJ and tested some combinations.
In the past I used to play with Xiom Diva koto top ply 85g, 5.7mm thickness and Hexer + Barracuda for some years. Tried Xiom Vega Europe and Pro as well, Europe was bottoming out too easily whereas Pro was a bit too hard.
For plastic ball I've slapped Hexer Grip and Hexer PowerGrip SFX on my good old Diva, it was ok except feel of too much flex on blocks.
Bought Xiom Offensive S, limba top ply 87g, 6.0mm and transferred rubbers to it, wow, it's quite a beast. Feels much faster despite limba top ply. Short game requires soft hand but blocks became considerably more consistent.
To be honest I rarely drive, mostly loop, even high balls close to the net, occasinally I smash high balls on my FH, but on BH i still prefer to loop, as my BH smash is too unreliable.
Also I've got a Tibhar Bernadette Szocs 1 7ply exactly to get a "slower" 7 ply, limba 85g 6.2mm thick again with Hexers but went a notch harder towards Powergip/Grip, no SFX versions. It indeed feels stiffer, loops and block require a bit more open angle due lower throw. I'd say it's in between Diva and Off S about speed. Short game is easier, I've noticed I began hitting flat more often and suddenly my BH slap started winning points. Also it's a bit easier to return balls when I am out of position, like reaching wide balls.
I still have no strict opinion which one is better for my game. I am going to play both Off S and BS1 for a while and then will see.